8.20.2005

The "Thrifty Gene" (It's not what you think)

I’ve spent the last couple of days reading about obese rats. There are several inbred species with funny names, like the Zucker Diabetic Fatty Rat or the Otsuka Long-Evans Tokushima Fatty Rat. But most interesting of all is a real species (as opposed to one engineered by the white coats): the Israeli Sand Rat, Psammomys Obesus. When observed in its natural, arid habitat—the deserts of North Africa and the Eastern Mediterranean—P. Obesus eats low-calorie salt bush, if it manages to find any food at all. But if caged in a laboratory and given an abundant food supply, the rats become obese within four days. After just four weeks of the new-found gluttony, they require insulin shots to stay alive.

So why study all these fat rats? Well, many researchers speculate that the lil’ critters store fat and acquire diabetes in the same way as the large percentage of obese humans who live in the Pacific Islands.

On the Micronesian island of Kosrae, for example, more than 80% of its 7,600 residents are overweight or obese, and one in eight adults have diabetes. But this wasn’t always the case. Until about fifty years ago, Kosraeans were a lean bunch who ate what they had—fish, bananas, and coconuts. Then, after World War II, the U.S. gained control and what do you know? Alluva sudden these thin, healthy folks were subjected to the evils of canned and processed foods—a new-found gluttony. And, just like the rats, they blew up.

Most smart people who study these things attribute the sudden weight changes to something called a “thrifty gene.” Some thousands of years ago, in the days of hunter-gathering, the ancestors of the obese Kosraeans had a “thrifty gene” that allowed them to store fat well. In those days famine was frequent, and the people with the gene could better survive the food shortages and pass the gene on to the next generation. Sort of like a hibernating bear who lives on his fat reserves in the winter. But today, when the islanders are faced with an abundant, high-fat food supply, the gene does more harm than good.

Here’s what I don’t get: why didn’t the Anglo-Saxon ancestors have this thrifty gene, too? Weren’t all of the hunter-gatherers exposed to devastating famine? Stay tuned…